The present specification, drawings and claims relate to fuel systems for small engines of the type less than about 25 horsepower (18.6 kilowatts) and which have found widespread use in garden tractors, riding mowers and portable power generating sets and other such appliances. Air cooled engines are widely used for such applications for compactness and reduced weight and may be closely cowled in certain of such applications. Engines employed in the aforesaid and other similar applications commonly have a fuel tank located proximate the engine and arranged for simplicity to have gravitational flow of fuel from the tank to the engine carburetor; however, in certain applications fuel pumps are employed.
In the above-mentioned small engine applications, the fuel tank is usually formed with a user removable cap or closure provided on a spud or filler tube extending from the tank; and, refueling is usually accomplished by manually pouring from a portable container and often requires use of a user provided funnel. The filler cap on such engine applications is typically provided with a vent passage for admitting make-up air into the tank as fuel is withdrawn during engine operation.
Recently it has been mandated that for such small engine applications fuel vapor emission to the atmosphere is prohibited and thus the use of such an open tank vent is not permissible. The entire fuel system must now be sealed to prevent fuel vapor escape to the atmosphere during periods of engine shutdown; and, it has further been required that the fuel vapor trapped in the system be stored and purged to the engine air inlet upon an engine operation. Thus, it has been necessary to add fuel vapor emission systems to small engine applications where heretofore no such requirements existed. This has particularly created problems where space is at a premium for compact or closely cowled air cooled engines.
In view of the extremely high volume mass production of small engines and the simplicity and commonality of the relatively small fuel tanks for such engines, it has been desired to provide a simple, easy to install and low cost vapor emission control system for such small engines and such a system which does not require redesign or retooling of the engine fuel tanks. Furthermore, it has been desired to provide fuel vapor emission control systems for small engines in a manner which has not significantly increased the volume of the fuel tank and engine in view of the space limitations in those applications and particularly where the engine is closely cowled.